1. Technical Field
This disclosure generally relates to illumination devices and more particularly to illumination devices to retrofit light fixtures as a replacement of gas-discharge lamps.
2. Description of the Related Art
Gas-discharge lamps are a family of artificial light sources that generate light by sending an electrical discharge through an ionized gas. Mercury-vapor lamps, a type of gas-discharge lamps and commonly referred to as “security lights”, use mercury in an excited state to produce light. The Energy Conservation Act of 2005 bans the manufacture and importation of mercury-vapor ballasts and luminaires. As a result, new ballasts for mercury-vapor type of luminaires are limited to the quantity of ballasts still existing in the inventory of manufacturers, distributors, and retail sales stores. Nevertheless, mercury-vapor bulbs can still be manufactured and imported in order to support the existing installed bases of luminaires of this type.
One reason for banning the manufacturing and importation of mercury-vapor lamp ballasts was that the combination of mercury-vapor ballasts and mercury-vapor bulbs results in energy inefficiency as well as a very low power factor. Power factor in an alternating-current (AC) electrical system is defined as the ratio of the “true power” to the “apparent power”, and is a number between 0 and 1. True power is the power dissipated by the luminaire. Apparent power is the total power that must be supplied to the luminaire including the power stored and returned to the power grid due to reactive components in the luminaire. Mercury-vapor lamps typically have a power factor of about 0.35 pf.
Additionally, mercury-vapor lamps emit light with a low color rendering index (CRI). For reference, sunlight has a CRI of 100 and represents “ideal light” in that it contains a continuous spectrum of visible radiation making all colors of an illuminated surface perceptible to the human eye. Light with a low CRI is less useful because illuminated surfaces are not all perceived as their true color. Light with a low CRI is also less pleasing to the eye, and less useful for discrimination of an illuminated scene. Mercury-vapor lamps have, on average, a very low CRI of approximately 35.
Another concern with mercury-vapor lamps is the long warm-up time required to achieve full output. The long startup time prohibits the effective use of motion-detecting sensors to automatically turn mercury-vapor luminaires ON when people, animals or other objects are present. For this reason, mercury-vapor luminaires are typically turned ON with an ambient light sensor that is triggered by the low level of light after sunset, and then left on all night. This is a very wasteful solution to the warm-up time problem which consumes large amounts of energy when no light is needed.
A mercury-vapor lamp typically has much higher energy consumption during the warm-up time than during normal operation. As much as 10 times the usual amount of current for normal operation is required during warm-up than normal operation. This can require expensive overdesign of the electrical wiring, especially when multiple mercury-vapor lamps may turn ON at the same time. For example, a load comprised of ten 175-Watt luminaires might consume 17,000 watts when turned ON within the warm-up times of the lamps.
Moreover, typical mercury-vapor luminaires have an optical design which results in as much as 40% of the emitted light escaping upward. This light and the energy consumed to produce such light are wasted because the escaping light is not directed toward the areas the luminaires are intended to illuminate. The upward escaping light is a source of “light trespass,” illuminating areas where the illumination is not desired. For example, such light pollutes the sky, causing problems for astronomers and others who wish to view the night sky.
Furthermore, mercury is a very toxic metal that contaminates landfills and water supplies when not disposed of properly, or when a mercury-vapor lamp is accidentally broken. Mercury is a restricted material and controlled by statute in most developed countries. Consequently, mercury-vapor lamps are expensive and troublesome to dispose of at end of life.
Other types of gas-discharge lamps, including high-pressure sodium-vapor lamps and metal halide lamps, have been developed to address some of the aforementioned problems. High-pressure sodium-vapor lamps are somewhat more energy efficient than mercury-vapor lamps, but still suffer from poor CRI and also contain mercury. Metal halide lamps are not commonly available to work with mercury-vapor lamp ballasts, and typically require a higher ignition voltage to start. Both high-pressure sodium-vapor lamps and metal halide lamps have similar warm-up and cool-down characteristics as mercury-vapor lamps. Neither corrects for the poor optical design of the security light luminaires. Both alternative types of lamps have poor power factors. Thus, none of these alternative gas-discharge lamps can serve as an ideal replacement of mercury-vapor lamps to fully address the aforementioned problems associated with mercury-vapor lamps.
Solid-state lighting, such as Light-emitting diode (LED) lighting, has been shown to be an energy-efficient alternative to gas-discharge lamps, and in general also tends to have longer service life than typical gas-discharge lamps. Many utilities and consumers thus find it economically compelling to replace gas-discharge lamps with LED replacement lamps. Typical area lighting luminaires include a metal housing, an electrical ballast, a lamp socket, and removable cover/refractor. LED replacement lamps for these luminaires typically have some form of active cooling system to remove the excess heat generated by the LEDs. Such an active cooling system, however, constitutes additional costs to the replacement lamp and requires an unobstructed air path to operate. On the other hand, LED lamps without cooling have been shown to have shorter service life due to the high temperatures that result from operating the LED lamp in the enclosed space of the luminaire's cover/refractor.